This invention relates to a method of fixedly mounting a timing gear on a crankshaft of an internal combustion engine.
In case of mounting a timing gear on a crakshaft, it is substantially necessary to mount the timing gear accurately on the crankshaft at a predetermined angle relationship relative to the crank pin thereof.
The conventional method of fitting the timing gear to the crankshaft comprises forming a keyway on the timing gear mounting portion of a crankshaft for indexing the angle of the timing gear, fitting a key to the keyway, engaging a keyway formed in the timing gear with the key and then sliding the former along the latter whereby rigidly mounting the timing gear on the crankshaft through the key at a predetermined angular relationship therebetween.
In such a structure, however, a torsional stress concentration due to a driving torque tends to occur on the bottom of the keyway of the crankshaft thereby causing a tendency of breakdown of the crankshaft along the keyway. Such a tendency is especially conspicuous in marine engines wherein the engine's output is taken out from the leading end portion of the crankshaft thereof by way of a pulley.